Car Won't Start - Head Gasket?

[avguy]

... "Clear Flood Mode" - I did try this but I don't see the butterfly in the throttle body move beyond the start position. .....

I've never watched the throttle plate on my Aveo like you did, so I can't say how far open it actually goes. However, pushing the pedal all the way down should always cause it to be as far open as it goes. If you have a realtime OBD scanner it should show close to 100% with the pedal all the way down. In any case, it appears it won't help get your vehicle started.

Based on what you wrote, I think its very likely that 2 cylinders are not firing at all. So it would appear that even though the 2 good cylinders are doing their best (sputtering), these small engines just can't get running on half power. Hope the HG repair goes well for you.